Fires, tank or pipe leaks, equipment failures, and other accidents often cause the inside of a building to become contaminated with toxic gases. Not only do such toxic gases endanger any workers or residents left inside, but they also hamper the efforts of emergency crews to enter the building and, for example, fight the fire. Moreover, it is usually not desirable simply to blow the gases out of the building, for example using large fans, since one does not wish to contaminate the area surrounding the contaminated building. Ideally, one would like to be able to remove the gases from the building but filter them so that they cannot escape to the atmosphere.
U.S. Pat. No. 3,766,844 (Donnelly et al., Oct. 23, 1973) describes a protective system for a contaminated atmosphere. This arrangement is intended to allow decontamination personnel to carry out decontamination procedures outside of a contaminated atmosphere but before entering a separate, protective shelter. The Donnelly system is both mechanically and electrically complicated, and includes a special pressure control module for preventing loss of pressurized protection when personnel enter and leave the shelter. Because of its complexity and its need for separate air compression, the Donnelly system is not well adapted for ready use with existing fire-fighting procedures.
Another shelter arrangement is described in U.S. Pat. No. 4,682,448 (Healy, Jul. 28, 1987). The shelter shown in this patent extends from an interior floor to a ceiling. A worker may set up a ladder within the Healy shelter and any debris or dust that falls from the ceiling as the worker works is either contained within the walls of the shelter or is vacuumed away by an attached vacuum cleaner. The Healy shelter is neither intended nor suited for eliminating dangerous contaminants from a contaminated building.
A "negative pressure" air filtering device, primarily intended for filtering out free asbestos and harmful industrial dusts, is described in U.S. Pat. No. 4,756,728 (Conrad, Jul. 12, 1988). The Conrad device is essentially a vacuum device, with a large, conical intake nozzle and internal filters. The Conrad device is not designed to work with the positive pressure procedures often used by those fighting fires and toxic contamination.
Positive pressure procedures typically produce much better air flow through the contaminated structure and any attached filtering device. Additionally, it is much easier to channel air using a positive pressure source than a negative pressure source. It is for example easy to aim a fan, but with a vacuum device at the filter outlet, air is sucked through the device without any practical means of directing its flow within the contaminated structure. Furthermore, unless attached filtering devices are rigid, negative pressure applied at their outer end to "suck" air out of a contaminated structure also often leads to collapse of the filtering device. Another example of a negative pressure filtration device is shown in U.S. Pat. No. 4,838,910 (Stollenwerk et al., Jun. 13, 1989).
The object of this invention is to provide a quickly and easily erected positive pressure arrangement for removing gaseous and particulate contaminants from a contaminated structure and for preventing them from escaping into the surrounding atmosphere.